Construction giant Grocon is due to meet union bosses at Fair Work Australia today as tensions rise over their ongoing dispute.

Hundreds of union members have gathered for the third day in a row at Grocon's Lonsdale Street site to vent their frustration with the company.

There were scuffles with mounted police on Tuesday, but since then the protests have been peaceful.

The Construction, Forestry, Mining and Energy Union (CFMEU) has organised the rallies and has vowed to continue its blockade despite a Supreme Court order not to further disrupt work.

The CFMEU says non-union members are being intimidated to prevent them from joining the union and say staff-elected safety officers are not allowed on the site.

Grocon says the illegal blockade is costing the company over $300,000 a day.

The State Government has asked the construction industry watchdog to prepare a report on the dispute.

Unionists in Sydney have staged similar protests and the parties in the Melbourne dispute are due to meet Fair Work Australia this afternoon.

Grocon's chief executive Daniel Grollo is reluctant to attend the talks but will go.

"I've got grave concerns of attending a meeting whilst the CFMEU across the country, in Brisbane, in Melbourne, in Sydney now; defying Supreme Court orders that are telling them to lift their illegal blockade."